The LastActive attribute provides inaccurate information (for example, offline for 180 days) about a contact's presence status in a Microsoft Skype for Business server 2015 environment. This issue occurs because of data loss after a user is moved from one pool to another pool. See KB3056287 for more information about the same issue in Skype for Business Online. This issue also occurs after you are re-homed on another Front End server in a same pool. For example, this issue occurs after a server patching.
To fix this issue, install the February 2017 cumulative update 6.0.9319.277 for Skype for Business Server 2015.